﻿254 
  INTRODUCTION 
  TO 
  BOTANY 
  

  

  of 
  these 
  plants 
  the 
  different 
  stages 
  were 
  thought 
  to 
  be 
  differ- 
  

   ent 
  plants, 
  and 
  were 
  so 
  named. 
  For 
  example, 
  tin- 
  rust 
  that 
  

   develops 
  on 
  leaves 
  of 
  the 
  apple 
  tree 
  early 
  in 
  the 
  spring 
  forms 
  

   spores. 
  These 
  spores 
  produce 
  the 
  parasite 
  known 
  as 
  cedar 
  

   apple 
  {Gymmsporangium), 
  which 
  grows 
  upon 
  cedar 
  trees. 
  

   Each 
  stage 
  produces 
  spores 
  which, 
  after 
  germinating 
  in 
  favor- 
  

   able 
  places, 
  produce 
  the 
  other 
  stage 
  of 
  the 
  rust. 
  1 
  

  

  Wheat 
  and 
  oat 
  rust 
  is 
  probably 
  the 
  best-known 
  and 
  most- 
  

   feared 
  member 
  of 
  the 
  rust 
  sub-division 
  of 
  fungi. 
  In 
  the 
  United 
  

   States 
  it 
  does 
  damage 
  to 
  our 
  wheat 
  and 
  oat 
  crops 
  every 
  year 
  tn 
  

   the 
  amount 
  of 
  at 
  least 
  $15,000,000, 
  and 
  probably 
  much 
  more. 
  

  

  The 
  first 
  conspicuous 
  appearance 
  of 
  rust 
  in 
  the 
  late 
  spring 
  

   or 
  early 
  summer 
  is 
  in 
  the 
  form 
  of 
  reddish-brown 
  patches 
  upon 
  

   stalks 
  and 
  leaves 
  of 
  wheat 
  and 
  oats 
  (fig. 
  198). 
  The 
  patches 
  are 
  

   composed 
  of 
  large 
  numbers 
  of 
  summer 
  spores 
  (iiredospores). 
  A 
  

   section 
  cut 
  through 
  the 
  host 
  leaf 
  enables 
  one 
  to 
  see 
  that 
  the 
  

   summer 
  spores 
  (fig. 
  198, 
  7>) 
  are 
  formed 
  upon 
  the 
  ends 
  of 
  hyphse. 
  

   The 
  spore-bearing 
  ends 
  of 
  hyplue 
  are 
  continuations 
  of 
  hyphie 
  

   which 
  have 
  pushed 
  their 
  way 
  among 
  the 
  leaf 
  cells 
  from 
  which 
  

   they 
  have 
  absorbed 
  their 
  nourishment. 
  At 
  the 
  time 
  summer 
  

   spores 
  are 
  formed, 
  the 
  host 
  plant 
  is 
  usually 
  thoroughly 
  infested 
  

   with 
  the 
  mycelium. 
  The 
  summer 
  sp< 
  ires 
  are 
  readily 
  carried 
  about 
  

   by 
  currents 
  of 
  air 
  or 
  by 
  contact 
  with 
  animals. 
  If 
  placed 
  upon 
  

   wheat 
  or 
  oat 
  plants, 
  these 
  spores 
  germinate 
  (fig. 
  198, 
  C) 
  and 
  

   the 
  young 
  hyphse 
  penetrate 
  the 
  host 
  and 
  product 
  1 
  new 
  mycelium. 
  

  

  Later 
  in 
  the 
  summer 
  the 
  same 
  mycelium 
  which 
  produced 
  

   summer 
  spores 
  produces 
  a 
  heavy-walled, 
  two-celled 
  spore 
  

   (fig. 
  198, 
  D*) 
  known 
  as 
  the 
  winter 
  spore 
  (teleutospore). 
  When 
  

   formed 
  in 
  large 
  quantities, 
  these 
  spores 
  appear 
  as 
  blistery 
  

   patches 
  much 
  like 
  those 
  made 
  by 
  the 
  reddish 
  summer 
  spores, 
  

   except 
  for 
  the 
  difference 
  in 
  color. 
  The 
  winter 
  spores 
  are 
  scat- 
  

   tered 
  over 
  the 
  ground 
  and 
  upon 
  wheat 
  and 
  oat 
  straw. 
  After 
  

  

  1 
  "The 
  Cedar-Apple 
  Fungi 
  and 
  Apple 
  Rust 
  in 
  Iowa," 
  Bulletin 
  84, 
  Iowa 
  

   Agr. 
  Exp. 
  Sta., 
  1905. 
  

  

  " 
  The 
  Asparagus 
  Rust 
  : 
  its 
  Treatment 
  and 
  Natural 
  Enemies," 
  Bulletin 
  129, 
  

   N. 
  J. 
  Agr. 
  Exp. 
  Sta., 
  1898. 
  

  

  